Conventional integrated circuits (IC) technology is often implemented to fabricate many semiconductor devices, such as field effect transistors (FETs), bipolar junction transistors (BJTs), diodes, and capacitors, at approximately a same level on a single integrated-circuit (IC) chip.
To integrate different semiconductor devices at approximately a same level on a single IC chip may have many disadvantages. For example, more lithography and other consequent process steps often need to be implemented to fabricate various devices individually in the advanced technology, which often increases the fabrication costs and complexity. In addition, expensive lithography processes are usually needed as the size of each device and the spacing between the devices decrease. Besides, it is complex and difficult to integrate various devices with different substrates or channel materials in the same level.